U.S. patent application number 10/562555 was filed with the patent office on 2006-10-19 for transmission method, transmission apparatus and communication system.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Kiyotaka Kobayashi, Akihiko Matsuoka, Yutaka Murakami, Masayuki Orihashi.
Application Number | 20060234729 10/562555 |
Document ID | / |
Family ID | 33554498 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060234729 |
Kind Code |
A1 |
Murakami; Yutaka ; et
al. |
October 19, 2006 |
Transmission method, transmission apparatus and communication
system
Abstract
Of any one of transmission method X of transmitting modulated
signal A and modulated signal B including the same data from a
plurality of antennas and transmission method Y of transmitting
modulated signal A and modulated signal B having different data
from the plurality of antennas, base station apparatus 201 does not
change the transmission method during data transmission and changes
only the modulation scheme. Base station apparatus 201 transmits
modulated signal A and modulated signal B to communication terminal
apparatus 251 using the determined transmission method and
modulation scheme. In this way, it is possible to improve data
transmission efficiency when transmitting data using the plurality
of antennas.
Inventors: |
Murakami; Yutaka;
(Yokohama-shi, JP) ; Kobayashi; Kiyotaka; (Ota-ku,
JP) ; Orihashi; Masayuki; (Funabashi-shi, JP)
; Matsuoka; Akihiko; (Yokohama-shi, JP) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
1615 L. STREET N.W.
SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
1006, Oaza Kadoma, Kadoma-shi
Osaka
JP
571-8501
|
Family ID: |
33554498 |
Appl. No.: |
10/562555 |
Filed: |
June 30, 2004 |
PCT Filed: |
June 30, 2004 |
PCT NO: |
PCT/JP04/09572 |
371 Date: |
December 28, 2005 |
Current U.S.
Class: |
455/462 |
Current CPC
Class: |
H04B 7/0689 20130101;
H04B 7/0697 20130101; H04L 1/06 20130101; H04B 7/0613 20130101;
H04B 7/0413 20130101; H04B 7/0608 20130101 |
Class at
Publication: |
455/462 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2003 |
JP |
2003-188898 |
Jun 28, 2004 |
JP |
2004-190418 |
Claims
1. A transmission method comprising: a transmission method
determining step of determining any one of a first transmission
method whereby a transmission apparatus provided with a plurality
of antennas transmits a plurality of signals including the same
data from a plurality of antennas and a second transmission method
whereby the transmission apparatus transmits a plurality of signals
including different data from the plurality of antennas; a
modulation scheme determining step of determining any one of the
plurality of modulation schemes; and a control step of controlling
whether or not determining processing should be performed in said
transmission method determining step and said modulation scheme
determining step in accordance with a communication procedure with
the other communication party.
2. The transmission method according to claim 1, wherein control is
performed in said control step so that determining processing is
not carried out in said transmission method determining step during
data transmission and determining processing is carried out only in
said modulation scheme determining step.
3. The transmission method according to claim 1, wherein the
modulation scheme used for said first transmission method and the
modulation scheme used for said second transmission method have the
same maximum value of the number of modulated M-ary index.
4. The transmission method according to claim 1, wherein in said
transmission method determining step, said first transmission
method or said second transmission method are determined based on a
channel fluctuation.
5. The transmission method according to claim 1, wherein a
transmission method to be used at the start of a communication is
predetermined in said transmission method determining step and a
modulation scheme to be used at the start of a communication is
predetermined in said modulation scheme determining step.
6. The transmission method according to claim 1, wherein control in
said control step is performed in such a way that determining
processing in said transmission method determining step is carried
out at longer time intervals than determining processing carried
out in said modulation scheme determining step.
7. The transmission method according to claim 1, wherein cyclic
delay diversity is used as said first transmission method in said
transmission method determining step.
8. The transmission method according to claim 1, wherein an
eigenmode in which singular vectors or eigen vectors of a channel
matrix in an MIMO system are used as channel signature vectors is
used as said first transmission method in said transmission method
determining step.
9. The transmission method according to claim 8, wherein said first
transmission method and said second transmission method are
switched in accordance with the number of other communication
parties in said transmission method determining step.
10. A radio communication system a comprising: a transmission
apparatus provided with a plurality of antennas;and a reception
apparatus that receives signals transmitted from the plurality of
antennas of said transmission apparatus, said reception apparatus
comprises: a channel fluctuation estimation section that estimates
a channel fluctuation about signals transmitted from the plurality
of antennas of the transmission apparatus; a transmission method
requesting section that determines any one of a first transmission
method of transmitting a plurality of signals including the same
data from the plurality of antennas and a second transmission
method of transmitting a plurality of signals including different
data from the plurality of antennas based on the estimated channel
fluctuation and requests the determined transmission method from
said transmission apparatus; a modulation scheme requesting section
that determines any one of a plurality of modulation schemes based
on the estimated channel fluctuation and requests the determined
modulation scheme from said transmission apparatus; and a control
section that controls whether or not the processing requested by
said transmission method requesting section and modulation scheme
requesting section should be performed in accordance with the
procedure for a communication with said transmission apparatus, and
said transmission apparatus comprises: a generation section that
generates a signal corresponding to the transmission method
requested from said reception apparatus; and a transmission
processing section that modulates a signal generated by said
generation section according to the modulation scheme requested
from said reception apparatus and transmits the modulated signal
from the respective antennas.
11. A transmission apparatus comprising a plurality of transmission
antennas; a transmission method determining section that determines
any one of a first transmission method of transmitting a plurality
of signals including the same data from the plurality of antennas
and a second transmission method of transmitting a plurality of
signals including different data from the plurality of antennas; a
modulation scheme determining section that determines any one of a
plurality of modulation schemes; a control section that controls
whether determining processing by said transmission method
determining section and modulation scheme determining section
should be performed or not in accordance with the procedure for a
communication with the other communication party; and a
transmission processing section that transmits the signals to which
said determined transmission method and modulation scheme are
applied from said plurality of antennas.
12. The transmission apparatus according to claim 11, wherein said
control section performs control in such a way that the
transmission method determining section does not perform
determining processing during data transmission and only the
modulation scheme determining section performs determining
processing.
13. The transmission apparatus according to claim 11, wherein said
transmission processing section adopts a modulation scheme having
the same maximum value of the number of modulated M-ary index for
the modulation scheme used for said first transmission method and
the modulation scheme used for said second transmission method.
14. The transmission apparatus according to claim 11, wherein said
transmission method determining section predetermines the
transmission method to be used at the start of a communication and
said modulation scheme determining section predetermines the
modulation scheme to be used at the start of a communication.
15. The transmission apparatus according to claim 11, wherein said
control section performs control in such a way that said
transmission method determining section performs determining
processing at longer time intervals than said modulation scheme
determining section performs determining processing.
16. The transmission apparatus according to claim 11, wherein said
transmission method determining section uses cyclic delay diversity
as said first transmission method.
17. The transmission apparatus according to claim 11, wherein said
transmission method determining section uses an eigenmode in which
singular vectors or eigen vectors of a channel matrix in an MIMO
system are used as channel signature vectors as said first
transmission method.
18. The transmission apparatus according to claim 17, wherein said
transmission method determining section switches between said first
transmission method and said second transmission method in
accordance with the number of other communication parties.
19. A reception apparatus comprising: a transmission method
determining section that determines any one of a first transmission
method of transmitting a plurality of signals including the same
data from a plurality of antennas and a second transmission method
of transmitting a plurality of signals including different data
from the plurality of antennas; a modulation scheme determining
section that determines any one of a plurality of modulation
schemes; a control section that controls whether the determining
processing by said transmission method determining section and
modulation scheme determining section should be performed or not in
accordance with the procedure for a communication with the other
communication party; and a requesting section that requests the
determined transmission method and modulation scheme from the other
communication party.
20. The reception apparatus according to claim 19, wherein said
control section performs control in such a way that the
transmission method determining section does not perform
determining processing during data reception and only the
modulation scheme determining section performs determining
processing.
21. The reception apparatus according to claim 19, further
comprising a channel fluctuation estimation section that estimates
both or any one of a channel fluctuation and reception field
intensity of the received signal, wherein said transmission method
determining section determines the transmission method based on the
estimation result estimated by said channel fluctuation estimation
section.
22. The reception apparatus according to claim 19, wherein the
modulation scheme used for said first transmission method and the
modulation scheme used for said second transmission method adopt
the same maximum value of the number of modulated M-ary index.
Description
TECHNICAL FIELD
[0001] The present invention relates to a transmission method,
transmission apparatus and communication system for transmitting
data from a plurality of antennas simultaneously.
BACKGROUND ART
[0002] Conventionally, a technology disclosed in "Space-Time Block
Codes from Orthogonal Design" IEEE Transactions on Information
Theory, pp. 1456 - 1467, vol. 45, no. 5, July 1999 is known as a
transmission method using a plurality of antennas. Hereinafter, the
contents disclosed in this document will be explained using
drawings.
[0003] FIG. 1 illustrates a conventional frame configuration. In
this figure, transmission signal A and transmission signal B are
signals transmitted from different antennas simultaneously.
Transmission signal A and transmission signal B are consist of a
symbol group containing the same data. SyA and SyB in the figure
denote symbols and "*" denotes a complex conjugate. Transmission
signal A is configured to form a frame of data symbols in an order
of SyA, to -SyB* and the transmission signal B is configured to
form a frame of data symbols in an order of SyB to SyA*. The
transmission signal A and transmission signal B are synchronized
with each other and transmitted. For this reason, data symbols SyA
and SyB are transmitted simultaneously and data symbols--SyB* and
SyA* are transmitted simultaneously.
[0004] FIG. 2 illustrates a conventional communication system.
Transmission apparatus 11 is provided with antenna 12 and antenna
13 and transmits, for example, transmission signal A shown in FIG.
1 from antenna 12 and transmission signal B from antenna 13 to
reception apparatus 21. Reception apparatus 21 receives the signals
transmitted from the antennas of transmission apparatus 11 by
antenna 22. The signal received by antenna 22 is a combination of
transmission signal A and transmission signal B, and therefore the
received signal is separated into transmission signal A and
transmission signal B and then demodulated.
[0005] In such a conventional communication system, transmission
apparatus 11 transmits transmission signal A from antenna 12 and
transmission signal B from antenna 13 and the signals transmitted
from the antennas are received by the reception apparatus via
different channel fluctuations (h1(t) and h2(t)). A conventional
communication system takes advantage of this and adopts frame
configuration shown in FIG. 1, and therefore, it is possible to
improve reception quality of reception apparatus 21.
[0006] However, in the above described conventional communication
system, SyA* and -SyB* are demodulated as SyA, SyB at the reception
apparatus, and information of SyA* and -SyB* are substantially the
same with SyA, SyB. This means that the same information is
transmitted twice, resulting in low data transmission
efficiency.
DISCLOSURE OF INVENTION
[0007] It is an object of the present invention to provide a
communication method, transmission apparatus and communication
system for improving data transmission efficiency when transmitting
data using a plurality of antennas.
[0008] It is possible to attain the above described object with a
transmission apparatus provided with a plurality of antennas, by
determining any one of a first transmission method of transmitting
a plurality of signals containing the same data from the plurality
of antennas respectively and a second transmission method of
transmitting a plurality of signals containing different data from
the plurality of antennas respectively based on channel
fluctuations between the transmitting and receiving sides and by
determining, when determining any one of a plurality of modulation
schemes, only a modulation scheme out of transmission methods and
modulation schemes from beginning to end of a communication.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 illustrates a conventional frame configuration;
[0010] FIG. 2 illustrates a conventional communication system;
[0011] FIG. 3A illustrates frame configurations of modulated signal
A and modulated signal B according to transmission method X;
[0012] FIG. 3B illustrates frame configurations of modulated signal
A and modulated signal B according to transmission method Y;
[0013] FIG. 4 is a schematic diagram showing a communication system
according to Embodiment 1 of the present invention;
[0014] FIG. 5 is a block diagram showing the configuration of a
transmission apparatus at a base station apparatus according to
Embodiment 1 of the present invention;
[0015] FIG. 6 is a block diagram showing the configuration of a
reception apparatus at a communication terminal apparatus according
to Embodiment 1 of the present invention;
[0016] FIG. 7A illustrates that a received signal has arrived on a
direct wave;
[0017] FIG. 7B illustrates that a received signal has arrived on
only a scattered wave without including any direct wave;
[0018] FIG. 8 illustrates a sequence diagram of a communication
procedure of the base station apparatus and communication terminal
apparatus according to Embodiment 1 of the present invention;
[0019] FIG. 9 illustrates changes with time of a transmission
method and a modulation scheme applied by the base station
apparatus according to Embodiment 1;
[0020] FIG. 10 illustrates a mode in which a transmission method
and a modulation scheme are changed;
[0021] FIG. 11 illustrates the number of transmission bits per unit
time according to a combination of transmission method X and
transmission method Y, and each modulation scheme;
[0022] FIG. 12 illustrates an input/output characteristic of an
amplifier;
[0023] FIG. 13 illustrates a sequence diagram of a communication
procedure of a base station apparatus and communication terminal
apparatus according to Embodiment 2 of the present invention;
[0024] FIG. 14 illustrates changes with time of a transmission
method and modulation scheme applied by the base station apparatus
according to Embodiment 2;
[0025] FIG. 15A illustrates a frame configuration of modulated
signal A and modulated signal B according to transmission method
X;
[0026] FIG. 15B illustrates a frame configuration of modulated
signal A and modulated signal B according to transmission method
Y:
[0027] FIG. 16A illustrates a frame configuration of transmission
method X;
[0028] FIG. 16B illustrates a frame configuration of transmission
method Y;
[0029] FIG. 17 is a block diagram showing the configuration of a
base station apparatus according to Embodiment 3 of the present
invention;
[0030] FIG. 18 is a block diagram showing the configuration of a
communication terminal apparatus according to Embodiment 3 of the
present invention;
[0031] FIG. 19 illustrates a sequence diagram of a communication
procedure of the base station apparatus and communication terminal
apparatus according to Embodiment 3 of the present invention;
[0032] FIG. 20 illustrates changes with time of a transmission
method and modulation scheme applied by the base station apparatus
according to Embodiment 3;
[0033] FIG. 21 illustrates a sequence diagram of a communication
procedure of a base station apparatus and communication terminal
apparatus according to Embodiment 4 of the present invention;
[0034] FIG. 22 illustrates changes with time of a transmission
method and modulation scheme applied by the base station apparatus
according to Embodiment 4;
[0035] FIG. 23 illustrates a frame configuration when CDD is
carried out using 12 symbols;
[0036] FIG. 24 illustrates the configuration of a channel
multiplexing communication system using a beam space mode
represented by an eigenmode in an MIMO system;
[0037] FIG. 25 illustrates the configuration of a transmission
apparatus of a base station apparatus according to Embodiment 6 of
the present invention;
[0038] FIG. 26A illustrates a point-to-multi point type
communication mode;
[0039] FIG. 26B illustrates a point-to-point type communication
mode;
[0040] FIG. 26C illustrates a point-to-point type communication
mode;
[0041] FIG. 27 illustrates an effect when a transmission method is
changed according to the number of other communication parties;
[0042] FIG. 28 illustrates an effect when a transmission method is
changed according to the number of other communication parties;
and
[0043] FIG. 29 illustrates a sequence diagram showing a
communication procedure of a base station apparatus and
communication terminal apparatus.
BEST MODE FOR CARRYING OUT THE INVENTION
[0044] With reference now to the accompanied drawings, embodiments
of the present invention will be explained below.
Embodiment 1
[0045] Frame Configuration
[0046] FIG. 3 illustrates frame configurations according to
Embodiment 1 of the present invention. FIG. 3A illustrates the
frame configurations of modulated signal A and modulated signal B
according to transmission method X and FIG. 3B illustrates the
frame configurations of modulated signal A and modulated signal B
according to transmission method Y. Channel condition estimation
symbol 101 and radio wave propagation environment estimation symbol
103 are symbols for a reception apparatus of the other
communication party to estimate a channel condition and called
"pilot symbol", "preamble", "control symbol", "predetermined
symbol", "unique word" or the like.
[0047] Transmission method reporting symbol 102 is a symbol showing
a transmission method (X or Y), modulation scheme, error correcting
scheme of a modulated signal transmitted from a base station
apparatus.
[0048] Data symbol 104 is user information such as audio data,
image data and character data transmitted from the base station
apparatus to a communication terminal apparatus.
[0049] Transmission Method X and Transmission Method Y
[0050] Transmission method X is a transmission method disclosed in
the above described document as in the case of the above described
conventional example for transmitting data symbols including the
same data (hereinafter referred to as "space-time coding") from two
antennas. As a specific example, from among data symbols SyA, SyB,
SyA*, -SyB* ("*" denotes a complex conjugate), modulated signal A
is composed of data symbols in an order of SyA and -SyB* and
modulated signal B is composed of data symbols in an order of SyB,
SyA*. On the other hand, information according to transmission
method Y is configured to form a frame from different data symbols.
As a specific example, from among data symbols SyA, SyB, SyC, SyD
which are information with different contents, modulated signal A
is composed of data symbols SyA and SyC and modulated signal B is
composed of data symbols SyB and SyD.
[0051] Note that both transmission method X and transmission method
Y shown in FIGS. 3A and 3B synchronize modulated signal A and
modulated signal B with each other and transmit them. For example,
according to transmission method X, data symbols -SyB* and SyA* are
transmitted simultaneously and according to transmission method Y,
data symbols SyC and SyD are transmitted simultaneously.
Furthermore, symbols of the same type of modulated signal A and
modulated signal B are also transmitted simultaneously.
[0052] FIG. 4 is a schematic diagram showing a communication system
according to Embodiment 1 of the present invention. In this figure,
base station apparatus 201 is provided with antenna 202 and antenna
203 and communicates with communication terminal apparatus 251 via
a radio channel. Communication terminal apparatus 251 is provided
with antenna 252 and antenna 253. This figure shows a situation
where base station apparatus 201 is transmitting a signal to
communication terminal apparatus 251.
[0053] Features of Transmission Method X and Transmission Method
Y
[0054] Here, suppose a channel condition in a channel fluctuation
between antenna 202 and antenna 252 is h11(t) and a channel
condition in a channel fluctuation between antenna 202 and antenna
253 is h12(t). Likewise, suppose a channel condition between
antenna 203 and antenna 252 is h21(t) and a channel condition
between antenna 203 and antenna 253 is h22(t). Here, t denotes
time. Channel conditions h11(t), h12(t), h21(t), h22(t) are
estimated by communication terminal apparatus 251 using channel
condition estimation symbol 101 and radio wave propagation
environment estimation symbol 103.
[0055] At this time, according to transmission method X, the
following equation holds: ( R .times. .times. 1 .times. ( i ) R
.times. .times. 1 .times. ( i + 1 ) ) = ( h .times. .times. 11
.times. ( i ) h .times. .times. 21 .times. ( i ) h .times. .times.
21 * ( i + 1 ) - h .times. .times. 11 * ( i + 1 ) ) .times. ( SyA
SyB ) ( 1 ) ##EQU1## where R1(t) is the received signal of antenna
252 shown in FIG. 4.
[0056] As is appreciated from this equation, according to
transmission method X, data symbols SyA and SyB are repeatedly
transmitted at times t=i and t=i+1. Here, a case where space-time
block codes are used is explained, but it is also possible to use
space-time trellis codes as exemplified in the following reference
document. (Reference document: "Space-Time Block Codes for High
Data Rate Wireless Communication: Performance Criterion and Code
Construction" IEEE Transactions on Information Theory, pp. 744-765,
vol. 44, no. 2, March 1998)
[0057] On the other hand, according to transmission method Y, the
following equation holds: ( R .times. .times. 1 .times. ( i ) R
.times. .times. 2 .times. ( i ) ) = ( h .times. .times. 11 .times.
( i ) h .times. .times. 12 .times. ( i ) h .times. .times. 21
.times. ( i ) h .times. .times. 22 .times. ( i ) ) .times. ( SyA
SyB ) ( 2 ) ##EQU2## where R1(t), R2(t) denote the received signals
of antennas 252 and 253 shown in FIG. 4.
[0058] As is appreciated from this equation, according to
transmission method Y, data symbols SyA and SyB are transmitted
only at time t=i.
[0059] As shown above, when transmission method X is compared with
transmission method Y, transmission method X has a lower
transmission rate than transmission method Y, yet has good
reception quality. On the contrary, transmission method Y has a
higher transmission rate than transmission method X, yet has a
tendency that reception quality deteriorates considerably.
Especially, transmission method Y has a property of deteriorating
reception quality severely when a direct wave is received. For this
reason, it may be considered that transmission method X is used
when a direct wave is received and transmission method Y is used
when a direct wave is not received.
[0060] Thus, determining transmission method X having high error
resistance, hence high reception quality or transmission method Y
having a high transmission rate according to the state of a channel
fluctuation makes it possible to improve both reception quality and
the transmission rate. That is, by switching the modulation scheme
as well as by switching between transmission method X and
transmission method Y, it is possible to further improve both
reception quality and the transmission rate.
[0061] Configuration of Transmission Apparatus at Base Station
Apparatus 201
[0062] FIG. 5 is a block diagram showing the configuration of a
transmission apparatus at base station apparatus 201 according to
Embodiment 1 of the present invention. In this figure, frame
generation instruction section 401 determines a transmission method
(X or Y) and modulation scheme (e.g., any one of QPSK, 16 QAM and
64 QAM) based on the transmission method request information and
modulation scheme request information transmitted from
communication terminal apparatus 251 and instructs the determined
contents to data sequence generation section 402, transmission
processing section 403 and transmission processing section 404 by
means of frame generation instruction signal S1.
[0063] Data sequence generation section 402 generates transmission
digital signal S2 of modulated signal A and transmission digital
signal S3 of modulated signal B in the frame configuration shown in
FIG. 3 from the transmission digital signal in accordance with the
instruction from frame generation instruction section 401.
Generated transmission digital signal S2 of modulated signal A is
output from data sequence generation section 402 to transmission
processing section 403 and generated transmission digital signal S3
of modulated signal B is output from data sequence generation
section 402 to transmission processing section 404.
[0064] Transmission processing section 403 and transmission
processing section 404 carry out transmission processing on
transmission digital signal S2 of modulated signal A output from
data sequence generation section 402 and transmission digital
signal S3 of modulated signal B output from data sequence
generation section 402, respectively according to the instructions
from frame generation instruction section 401. Since transmission
processing section 403 and transmission processing section 404 have
the same internal configuration, the configuration of transmission
processing section 403 will be explained below.
[0065] Modulation section 4031 is capable of modulating under a
plurality of modulation schemes and modulates transmission digital
signal S2 of modulated signal A output from data sequence
generation section 402 under the modulation scheme instructed from
frame generation instruction section 401. Modulated signal S4 is
output from modulation section 4031 to spreading section 4032.
[0066] Spreading section 4032 multiplies signal S4 output from
modulation section 4031 by a spreading code and outputs spread
modulated signal A to radio section 4033 and radio section 4033
carries out predetermined radio processing (D/A conversion or
up-conversion or the like) on spread signal S5 and outputs signal
S6 after the radio processing to amplifier 4034.
[0067] Amplifier 4034 amplifies the power of signal S6 output from
radio section 4033 and transmits power-amplified signal S7 from
antenna 202 to communication terminal apparatus 251.
[0068] Configuration of Reception Apparatus at Communication
Terminal Apparatus 251
[0069] FIG. 6 is a block diagram showing the configuration of a
reception apparatus at communication terminal apparatus 251
according to Embodiment 1 of the present invention. In this figure,
antenna 252 receives signal S51 combining the signals transmitted
from antenna 202 and antenna 203 of base station apparatus 201 and
radio section 501 carries out predetermined radio processing
(down-conversion and A/D conversion or the like) on signal S51
received by antenna 252 and outputs signal S52 after the radio
processing to despreading section 502.
[0070] Despreading section 502 multiplies signal S52 output from
radio section 501 by a spreading code and carries out despreading.
Despread signal S53 is output from despreading section 502 to frame
synchronization section 503, first channel fluctuation estimation
section 504, second channel fluctuation estimation section 505,
demodulation section 510 and reception field intensity estimation
section 511.
[0071] Frame synchronization section 503 achieves frame
synchronization between modulated signal A and modulated signal B
based on signal S53 output from despreading section 502 and signal
S56 output from despreading section 507 and forms timing signal
S57. Timing signal S57 is output from frame synchronization section
503 to first channel fluctuation estimation sections 504 and 508,
second channel fluctuation estimation sections 505 and 509 and
demodulation section 510.
[0072] First channel fluctuation estimation section 504 estimates a
channel fluctuation of modulated signal A, that is, estimates a
channel condition according to timing signal S57 output from frame
synchronization section 503 using channel condition estimation
symbol 101 of modulated signal A and radio wave propagation
environment estimation symbol 103 out of signal S53 output from
despreading section 502. The estimated channel fluctuation
information of modulated signal A is output as channel fluctuation
estimation signal S58 from first channel fluctuation estimation
section 504 to demodulation section 510 and eigenvalue calculation
section 512. Channel fluctuation estimation signal S58 of modulated
signal A corresponds to h11(t) of Equation (2).
[0073] Second channel fluctuation estimation section 505 estimates
a channel fluctuation of modulated signal B (channel condition)
according to timing signal S57 output from frame synchronization
section 503 using channel condition estimation symbol 101 of
modulated signal B and radio wave propagation environment
estimation symbol 103 out of signal S53 output from despreading
section 502. The estimated channel fluctuation information of
modulated signal B is output as channel fluctuation estimation
signal S59 from second channel fluctuation estimation section 505
to demodulation section 510 and eigenvalue calculation section 512.
Channel fluctuation estimation signal S59 of modulated signal B
corresponds to h12(t) of Expression (2).
[0074] Signal S54 received by antenna 253 is subjected to
processing similar to that described above by radio section 506,
despreading section 507, first channel fluctuation estimation
section 508 and second channel fluctuation estimation section 509,
and therefore detailed explanations thereof will be omitted. Note
that channel fluctuation estimation signal S60 output from first
channel fluctuation estimation section 508 to demodulation section
510 corresponds to h21(t) of Equation (2) and channel fluctuation
estimation signal S61 output from second channel fluctuation
estimation section 509 to demodulation section 510 corresponds to
h22(t) of Equation (2).
[0075] Demodulation section 510 demodulates signals S53 and S56
output from despreading section 502 and despreading section 507
according to timing signal S57 output from frame synchronization
section 503 using channel fluctuation estimation signals S58, S59,
S60 and S61 output from first channel fluctuation estimation
sections 504 and 508, second channel fluctuation estimation
sections 505 and 509 and obtains a received digital signal of
modulated signal A and a received digital signal of modulated
signal B. At this time, demodulation section 510 acquires a
transmission method (X or Y), modulation scheme and error
correcting scheme of the signal from transmission method reporting
symbol 102 of signals S53, S56 output from despreading section 502
and despreading section 507 and demodulates the data symbols
according to the acquired contents.
[0076] Reception field intensity estimation section 511 estimates
reception field intensity based on signals S53 and S56 output from
despreading section 502 and despreading section 507 and outputs the
estimation result as reception field intensity estimation signal
S62 to modulation scheme determining section 513 and transmission
method determining section 514. The reception field intensity
referred to here means effective carrier power. Furthermore, with
regard to the channel fluctuation estimation sections such as first
channel fluctuation estimation sections 504, 508 and second channel
fluctuation estimation sections 505, 509 and reception field
intensity estimation section 511, any one or both of the channel
fluctuation estimation sections and reception field intensity
estimation section 511 function as the channel fluctuation
estimation section.
[0077] When channel fluctuation information output from first
channel fluctuation estimation sections 504 and 508 and second
channel fluctuation estimation sections 505 and 509 is assumed to
be a channel matrix as shown in Equation (2), eigenvalue
calculation section 512 calculates the eigenvalue. The calculated
eigenvalue is output as eigenvalue signal S63 from eigenvalue
calculation section 512 to modulation scheme determining section
513 and transmission method determining section 514.
[0078] Modulation scheme determining section 513 as a modulation
scheme requesting section determines the modulation scheme to be
requested from base station apparatus 201 based on reception field
intensity estimation signal S62 output from reception field
intensity estimation section 511 and eigenvalue signal S63 output
from eigenvalue calculation section 512 and outputs the modulation
scheme as modulation scheme request information. Note that the
modulation scheme may also be determined only based on reception
field intensity and in this case, influences on the transmission
rate and transmission quality are small.
[0079] Transmission method determining section 514 as a
transmission method requesting section determines transmission
method X or transmission method Y applied by base station apparatus
201 when a communication is started based on eigenvalue signal S63
output from eigenvalue calculation section 512 and estimation
signal S62 (reception field intensity) output from reception field
intensity estimation section 511. The determined information is
output from communication terminal apparatus 251 as transmission
method request information. Taking the case of Equation (2) as an
example to explain more specifically, eigenvalue signal S63 output
from eigenvalue calculation section 512 includes two eigenvalues
and a difference in the magnitude of eigenvalue is calculated
assuming that these two eigenvalues are .lamda.1, .lamda.2
(|.lamda.1(t)|>|.lamda.2(t)|). That is,
|.lamda.1(t)|.sup.2-|.lamda.2(t)|.sup.2 is calculated. When this
difference is greater than a predetermined value, transmission
method X is determined assuming that a direct wave is received. On
the contrary, when this difference is smaller than the
predetermined value, transmission method Y is determined assuming
that only a scattered wave including no direct wave is received. In
this respect, the calculation result of
|.lamda.1(t)|.sup.2-|.lamda.2(t)|.sup.2 reflects the state of a
probability density distribution of eigenvalues.
[0080] Method of Deciding Whether or Not Received Signal is
Arriving on Direct Wave
[0081] The method of deciding whether or not a received signal is
arriving on a direct wave will be explained using FIG. 7. First,
tan.sup.-1(Q/I) is calculated from an I component and a Q component
of a received baseband signal. FIG. 7 is a figure expressing
tan.sup.-1(Q/I) on the horizontal axis and probability density on
the vertical axis. FIG. 7A illustrates a case where a direct wave
has been received and a high probability that a peak appears in the
phase of a direct wave is high. On the other hand, FIG. 7B
illustrates a case where only a scattered wave including no direct
wave has been received and probability that a peak appears is low.
In this way, it is possible to determine whether or not a direct
wave has been received by calculating a probability density of
tan.sup.-1(Q/I) and deciding how it is distributed.
[0082] Furthermore, two eigenvalues of a 2.times.2 matrix
(hereinafter referred to as "channel matrix") expressed by the
channel condition component of above described Equation (2) are
obtained and if the eigenvalues are expressed by .lamda.1, .lamda.2
(|.lamda.1|>|.lamda.2|), the presence or absence of a received
direct wave is reflected in the relationship between .lamda.1 and
.lamda.2. For this reason, it is possible to decide whether or not
a direct wave has been received based on an eigenvalue of a channel
matrix. More specifically, it is possible to express the magnitude
of the eigenvalue with a probability density distribution and the
reception quality depends on the distribution of the eigenvalue,
and therefore it is possible to decide whether or not reception
quality corresponds to the quality when a direct wave has been
received based on the distribution of the eigenvalue.
[0083] Transmission Method and Modulation Scheme Applied to
Transmission Method Report Symbol
[0084] Transmission method reporting symbol 102 is the information
to report the transmission method of a modulated signal, modulation
scheme and error correcting scheme. It is difficult to demodulate
data unless this transmission method reporting symbol 102 is
demodulated correctly and therefore, it is desirable to transmit
transmission method reporting symbol 102 using transmission method
X and BPSK as the modulation scheme. Furthermore, it is further
desirable to incorporate error correction. This makes it possible
to improve the error resistance of transmission method reporting
symbol 102 and also improve the demodulation accuracy of this
symbol and therefore, communication terminal apparatus 251 is
capable of acquiring the transmission method, modulation scheme and
error correcting scheme correctly. Therefore, base station
apparatus 201 can transmit information about the transmission
method, modulation scheme and error correcting scheme of data
symbol 104 to communication terminal apparatus 251 correctly and
avoid the situation where communication terminal apparatus 251
cannot demodulate data.
[0085] Furthermore, for example, even when transmission method Y is
determined at the beginning of a communication, it is possible to
transmit the modulation scheme and error correcting scheme
accurately by transmitting a transmission method report symbol
using transmission method X, which result in improving the
reception quality. Since both transmission method X and
transmission method Y have two systems of modulated signals to be
transmitted, the transmission method is changed, that is,
transmission method Y is changed to transmission method X without
changing the number of antennas of the transmission apparatus of
the base station apparatus. Therefore, no change is involved in the
hardware of the radio apparatus and a transmission method reporting
symbol is transmitted accurately and reception quality of the data
can be improved easily.
[0086] Operations of Base Station Apparatus 201 and Communication
Terminal Apparatus 251
[0087] FIG. 8 is a sequence diagram showing the communication
procedure of base station apparatus 201 and communication terminal
apparatus 251 according to Embodiment 1 of the present invention.
In this figure, in step (hereinafter abbreviated as "ST") 601,
communication terminal apparatus 251 requests base station
apparatus 201 to start a communication and base station apparatus
201 receives this request.
[0088] In ST602, base station apparatus 201 reports to
communication terminal apparatus 251 that a request to start a
communication is received in ST601. At this time, channel condition
estimation symbol 101 shown in FIG. 3 is also transmitted
together.
[0089] In ST603, communication terminal apparatus 251 estimates a
channel condition using channel condition estimation symbol 101
transmitted in ST602, determines the transmission method (X or Y)
of the modulated signal and modulation scheme transmitted by base
station apparatus 201 based on the eigenvalue of the channel matrix
expressed by Equation (2) and requests the determined transmission
method and modulation scheme from base station apparatus 201. Base
station apparatus 201 receives this request.
[0090] In ST604, base station apparatus 201 determines the
transmission method and modulation scheme based on the requests for
the transmission method and modulation scheme transmitted from
communication terminal apparatus 251 and transmits the determined
transmission method and modulation scheme to communication terminal
apparatus 251 using transmission method reporting symbol 102.
[0091] In ST605, base station apparatus 201 transmits radio wave
propagation environment estimation symbol 103 and data symbol 104
to communication terminal apparatus 251 using the transmission
method and modulation scheme determined in ST604 according to the
frame configuration shown in FIG. 3.
[0092] In ST606, during a communication with base station apparatus
201, communication terminal apparatus 251 determines only the
modulation scheme again based on radio wave propagation environment
estimation symbol 103 and requests the determined modulation scheme
from base station apparatus 201. Base station apparatus 201
receives this request.
[0093] In ST607, base station apparatus 201 determines only the
modulation scheme again based on the request transmitted from
communication terminal apparatus 251 and notifies the modulation
scheme of communication terminal apparatus 251 using transmission
method reporting symbol 102.
[0094] In ST608, base station apparatus 201 transmits radio wave
propagation environment estimation symbol 103 and data symbol 104
to communication terminal apparatus 251 using the modulation scheme
determined in ST607 according to the frame configuration shown in
FIG. 3.
[0095] In ST609, base station apparatus 201 reports an end of
communication to communication terminal apparatus 251 and
communication terminal apparatus 251 receives this report and
finishes the communication.
[0096] Method of Changing Transmission Method and Modulation
Scheme
[0097] In the above described series of communication procedures,
FIG. 9 shows how the transmission method and modulation scheme
applied by base station apparatus 201 change with time-shift. Here,
three modulation schemes QPSK, 16 QAM, 64 QAM are supposed to be
used. In this figure, it is supposed that a communication between
base station apparatus 201 and communication terminal apparatus 251
starts at time t0 and transmission method X and QPSK are used from
time t1 to t2. At time t2, only the modulation scheme is changed
from QPSK to 16 QAM and from time t2 to t3, transmission method X
and 16 QAM are used. Furthermore, at time t3, only the modulation
scheme is changed again from 16 QAM to 64 QAM. From time t3 to t4,
transmission method X and 64 QAM are used and the communication
ends at time t5.
[0098] Furthermore, at time t6, when base station apparatus 201 and
communication terminal apparatus 251 start a communication,
transmission method Y and 64 QAM are supposed to be used from time
t7 to t8. At time t8, only the modulation scheme is changed from 64
QAM to 16 QAM and transmission method Y and modulation scheme 16
QAM are used from time t8 to t9. Furthermore, at time t9, only the
modulation scheme is changed again from 16 QAM to QPSK. From time
t9 to t10, transmission method Y and QPSK are used and the
communication ends at time t11.
[0099] Note that the changes of the modulation scheme at times t2,
t3, t8 and t9 are the results of reflecting the modulation scheme
request in ST606 shown in FIG. 8 and the modulation scheme is
changed according to the radio wave propagation environment.
[0100] Thus, the transmission method is determined at the beginning
of the communication and the transmission method is not changed
from start to end of the communication and only the modulation
scheme is changed.
[0101] Method of Changing Transmission Method and Modulation Scheme
Other than Methods Shown in FIG. 9
[0102] In addition to the method of changing the transmission
method and modulation scheme shown in FIG. 9, the change method
shown in FIG. 10 can also be considered. FIG. 10 will be explained
below.
[0103] In FIG. 10, a communication between the base station
apparatus and communication terminal apparatus starts at time t0
and transmission method X and QPSK are used from time t1 to t2. At
time t2, transmission method X is changed to transmission method Y
and the modulation scheme is changed from QPSK to 16 QAM. At time
t3, transmission method Y is changed to transmission method X and
the modulation scheme is changed from 16 QAM to 64 QAM. At time t4,
only the transmission method is changed from X to Y and at time t5,
only the modulation scheme is changed from 64 QAM to 16 QAM. At
time t7, the communication ends.
[0104] In this way, both the transmission method and modulation
scheme may be changed during a communication in accordance with the
radio wave propagation environment. However, such a change method
increases the number of combinations (hereinafter simply referred
to as "combinations") that can be selected when the change takes
place, which results in a more complicated system. That is, when
one out of many combinations is selected, it is necessary to
estimate a radio wave propagation environment with high accuracy
and a combination which is not suitable for the radio wave
propagation environment may be selected unless high accuracy
estimation is performed, which may deteriorate reception
quality.
[0105] Furthermore, if the estimation accuracy of the radio wave
propagation environment is improved, a combination suitable for the
radio wave propagation environment may be selected, but when the
communication terminal apparatus performs high accuracy estimation,
the stability of the system depends on the estimation accuracy of
the radio wave propagation environment of the communication
terminal apparatus and it is more difficult to reduce the size of
the terminal apparatus and reduce power consumption.
[0106] Therefore, as shown in FIG. 9, only changing the modulation
scheme without changing the transmission method during a
communication will save the base station apparatus and
communication terminal apparatus a complicated communication
procedure. Furthermore, it is also possible to alleviate the
estimation accuracy of the radio wave propagation environment of
the communication terminal apparatus, reduce the size and power
consumption of the communication terminal apparatus and prevent the
processing load of the overall system increasing.
[0107] In this respect, even when the transmission method is not
changed during a communication, the propagation model does not
change drastically. Furthermore, transmission method Y has a high
data transmission rate, but its propagation model has a
considerable influence on the reception quality.
[0108] Modulation Scheme to be Combined with Transmission Method X
or Transmission Method Y
[0109] FIG. 11 illustrates the number of transmission bits per unit
time by a combination of transmission method X and transmission
method Y and each modulation scheme. Transmission method Y can
transmit twice as many transmission bits as those of transmission
method X under each modulation scheme. Here, it is necessary to
realize a combination of transmission method X with 4096 QAM in
order that transmission method X can also obtain the same amount of
transmission bits per unit time transmitted as transmission method
Y.
[0110] However, the reception quality when 4096 QAM is adopted for
transmission method X is lower than the reception quality of when
64 QAM is adopted for transmission method Y. For this reason, to
improve both the reception quality and transmission rate, it is not
desirable to realize 4096 QAM using transmission method X.
[0111] Furthermore, input and output characteristics of amplifiers
4034 and 4044 of base station apparatus 201 shown in FIG. 5 will be
considered using FIG. 12. FIG. 12 illustrates an input and output
characteristic of the amplifier. In this figure, it is premised
that the horizontal axis shows an input level and the vertical axis
shows an output level, the input range of QPSK is A1, the input
range of 64 QAM is A2 and the input range of 4096 QAM is A3. In
addition, two different input and output characteristics are shown
with a solid line and dotted line respectively. Suppose the
amplifier having the input and output characteristic shown with the
solid line (hereinafter referred to as "amplifier P1") has a range
of A2 and the amplifier having the input and output characteristic
shown with the dotted line (hereinafter referred to as "amplifier
P2") has a range of A3. Note that if the modulation scheme is
unchanged, the amplitude variation range of a modulated signal,
that is, the input range is also unchanged irrespective of the
transmission method. Furthermore, the amplitude variation range of
a modulated signal generally increases as the number of modulated
M-ary index increases.
[0112] Using amplifier P1 is sufficient if the maximum number of
modulated M-ary index is 64 QAM with transmission method Y. On the
contrary, in order that transmission method X realizes the
transmission rate that is realized by using a combination of
transmission method Y and 64 QAM, it is necessary to use the
modulation scheme of 4096 QAM, and in this case, amplifier P2 must
be used. The output characteristic of amplifier P2 extends over a
wider range of the output level than the output characteristic of
amplifier P1 and the reception apparatus needs to process a signal
having a wider range of variation, and therefore the reception
apparatus needs to secure linearity of this signal, which
complicates the circuit configuration.
[0113] Furthermore, since amplifier P2 consumes greater power than
amplifier P1, it has lower power efficiency and has the larger
scale of the amplifier itself.
[0114] From this, it is desirable to equalize the maximum number of
modulated M-ary index of the modulation scheme to be combined with
transmission method X or transmission method Y. This makes it
possible to suppress power consumption of the transmission
apparatus and simplify the circuit configuration of the reception
apparatus.
[0115] Maximum Value of Number of Modulated M-Ary Index when the
Number of Transmission Antennas is 4
[0116] When the above described case with two transmission antennas
is changed to a case with four transmission antennas, where
modulated signals are transmitted from four transmission antennas,
it is not necessary for the reception apparatus to process a signal
having a wide variation range by setting a smaller maximum value of
the number of modulated M-ary index with four transmission antennas
than the maximum value of the number of modulated M-ary index with
two transmission antennas, and therefore it is possible to simplify
the circuit configuration of the reception apparatus.
[0117] Explanations of the above described number of modulated
M-ary index are not limited to a single carrier scheme but the same
applies to a case where a multicarrier scheme including an OFDM
scheme is used. Furthermore, a spread spectrum scheme may be used
or may not be used.
[0118] Thus, according to this embodiment, the base station
apparatus and communication terminal apparatus are provided with a
plurality of antennas respectively, the base station apparatus
determines any one of transmission method X whereby modulated
signal A and modulated signal B including the same data are
transmitted from a plurality of antennas and transmission method Y
whereby modulated signal A and modulated signal B including
different data are transmitted from a plurality of antennas at the
beginning of a communication, does not change the transmission
method during the communication and only changes the modulation
scheme, and can thereby improve both the data transmission rate and
transmission quality.
[0119] In this embodiment, the communication terminal apparatus
estimates a propagation model using channel condition estimation
symbols transmitted from the base station apparatus at the
beginning of a communication and requests a transmission method.
And it is also possible that the communication terminal apparatus
receives radio wave propagation environment estimation symbols and
data symbols transmitted by the base station apparatus when the
base station apparatus is communicating with the other
communication terminal apparatus and requests the transmission
method at the beginning of a communication. This eliminates the
necessity for inserting channel condition estimation symbols into a
frame, and can thereby further increase the data transmission
rate.
[0120] Furthermore, in this embodiment, the communication terminal
apparatus determines a transmission method and modulation scheme
based on eigenvalues and reception field intensity, but the present
invention is not limited to this, and can also determine a
transmission method and modulation scheme based on at least one of
a bit error rate, packet loss rate and frame error rate, and
reception field intensity. For example, transmission method X may
be determined when the reception field intensity is strong, but the
bit error rate is high.
Embodiment 2
[0121] Embodiment 1 has explained the case where the transmission
method is not changed during a communication, but this embodiment
will explain a case where a transmission method is changed during a
communication.
[0122] The configurations of a base station apparatus and
communication terminal apparatus in this embodiment are the same as
those of Embodiment 1, and therefore FIG. 5 and FIG. 6 will be used
again and detailed explanations thereof will be omitted.
[0123] FIG. 13 illustrates a sequence diagram of a communication
procedure of the base station apparatus and communication terminal
apparatus according to Embodiment 2 of the present invention.
However, ST1101 to ST1108 in this figure are the same as ST601 to
ST608 in FIG. 8 and ST1111 to ST1114 are the same as ST605 to
ST608, and therefore detailed explanations thereof will be
omitted.
[0124] In ST1109, the communication terminal apparatus estimates a
channel condition using channel condition estimation symbols
transmitted from the base station apparatus and determines a
transmission method and modulation scheme applied by the base
station apparatus during a communication based on the eigenvalues
of the channel matrix shown by Equation (2) in Embodiment 1. The
communication terminal apparatus requests the determined
transmission method and modulation scheme from the base station
apparatus. The base station apparatus receives this request.
[0125] In ST1110, the base station apparatus determines a
transmission method and modulation scheme based on the request
transmitted from the communication terminal apparatus and notifies
the communication terminal apparatus of the determined combination
using transmission method report symbols.
[0126] In ST1115, the base station apparatus reports end of a
communication to the communication terminal apparatus and the
communication terminal apparatus receives this report, and then the
communication ends.
[0127] In such a series of communication procedures, FIG. 14
illustrates changes with time-shift of a transmission method and
modulation scheme applied by the base station apparatus. Here,
three modulation schemes QPSK, 16 QAM, 64 QAM are supposed to be
used. In this figure, suppose a communication between the base
station apparatus and communication terminal apparatus starts at
time t0 and transmission method X and QPSK are used from time t1 to
t2. At time t2, only the modulation scheme is changed from QPSK to
16 QAM and transmission method X and 16 QAM are used from time t2
to t3. Furthermore, at time t3, only the modulation scheme is
changed again from 16 QAM to 64 QAM. Transmission method X and 64
QAM are used from time t3 to t4.
[0128] At time t4, the communication terminal apparatus requests to
change the transmission method and modulation scheme, requesting to
change the transmission method to transmission method Y and
maintain the modulation scheme of 64 QAM.
[0129] At time t5, the transmission method is changed during a
communication from transmission method X to transmission method Y
and the modulation scheme is kept to 64 QAM. Transmission method Y
and 64 QAM are used from time t5 to t6.
[0130] At time t6, only the modulation scheme is changed from 64
QAM to 16 QAM and transmission method Y and modulation scheme 16
QAM are used from time t6 to t7. Furthermore, at time t7, only the
modulation scheme is changed again from 16 QAM to QPSK.
Transmission method Y and QPSK are used from time t7 to t8 and the
communication ends at time t9.
[0131] In this way, by changing the transmission method during a
communication at predetermined time intervals, it is possible to
respond to changes of a propagation path model. Note that the
predetermined time interval is such an interval that transmission
methods are not changed unnecessarily.
[0132] In this way, according to this embodiment, when a
communication time takes a long time, the propagation model may
change, and therefore, it is possible to improve both reception
quality and the increase of transmission rate even when the
propagation model is changed during the communication by changing
the transmission method during a communication.
[0133] This embodiment may also be adapted so as not to estimate a
propagation model at the start of a communication, to forcibly
start a communication using transmission method X and estimate the
propagation model using radio wave propagation environment
estimation symbols during the communication. This eliminates the
necessity for inserting channel condition estimation symbols in a
frame, and can thereby further increase the data transmission
rate.
[0134] Furthermore, Embodiment 1 and Embodiment 2 have explained
the spread spectrum communication scheme, but the present invention
is not limited to this and can be likewise implemented under a
single carrier scheme with the spreading section removed or under
an OFDM scheme.
Embodiment 3
[0135] Embodiment 1 explains the case of the spread spectrum
communication scheme, but Embodiment 3 will explain a case where a
transmission method and modulation scheme are fixed at the
beginning of a communication under an OFDM scheme.
[0136] FIG. 15 illustrates the frame configuration of Embodiment 3
of the present invention. Components common to FIG. 15 and FIG. 3
are assigned the same reference numerals as those in FIG. 3 and
detailed explanations thereof will be omitted. As shown in FIG. 15,
the OFDM scheme is to arrange symbols not only in a time direction
but also in a frequency direction, and here, the number of carriers
is supposed to be 4. On each carrier, transmission method reporting
symbol 102, radio wave propagation environment estimation symbol
103 and data symbol 104 are arranged in that order.
[0137] FIG. 15A illustrates the frame configurations of modulated
signal A and modulated signal B using transmission method X.
Focused on carrier 1, it has the same arrangement of data symbols
as an arrangement shown in FIG. 3A and transmits data symbols in
such an arrangement. Data symbols with the same reference numerals
as those of carrier 1 are also arranged on carriers 2 to 4, which
transmit the arranged data symbols.
[0138] FIG. 15B shows the frame configurations of modulated signal
A and modulated signal B using transmission method Y. Focused on
carrier 1, it has the same arrangement of data symbols as that
shown in FIG. 3B and carrier 1 transmits data symbols with
different information contents. Data symbols with different
information contents are also arranged on carriers 2 to 4 as in the
case of carrier 1 and carriers 2 to 4 transmit the arranged data
symbols.
[0139] FIG. 15 has shown the case of an OFDM scheme in which data
symbols are coded in a time area, but as shown in FIG. 16, this
embodiment is also applicable to a case of an OFDM scheme in which
data symbols are coded in a frequency area. FIG. 16A shows the
frame configuration of transmission method X and FIG. 16B shows the
frame configuration of transmission method Y. At this time, in
antenna 252 shown in FIG. 4, assuming that a received signal on
carrier 1 and at time t is R1(t,1) and a received signal on carrier
2 and at time t is R1(t,2). Then, the following equation holds: ( R
.times. .times. 1 .times. ( i , 1 ) R .times. .times. 1 .times. ( i
, 2 ) ) = ( h .times. .times. 11 .times. ( i ) h .times. .times. 21
.times. ( i ) h .times. .times. 21 * ( i ) - h .times. .times. 11 *
( i ) ) .times. ( SyA SyB ) ( 3 ) ##EQU3##
[0140] Similar coding can also be applied to carrier 3 and carrier
4.
[0141] FIG. 17 is a block diagram showing the configuration of a
base station apparatus according to Embodiment 3 of the present
invention. Note that components of FIG. 17 common to FIG. 5 are
assigned the same reference numerals as those in FIG. 5 and
detailed explanations thereof will be omitted. In this figure, data
sequence generation section 1401 generates transmission digital
signal S72 of modulated signal A and transmission digital signal
S73 of modulated signal B corresponding to the frame configuration
shown in FIG. 15 from a transmission digital signal in accordance
with an instruction (frame generation instruction signal S71) from
frame generation instruction section 401. Generated transmission
digital signal S72 of modulated signal A is output from data
sequence generation section 1401 to transmission processing section
1402 and generated transmission digital signal S73 of modulated
signal B is output to transmission processing section 1405.
[0142] Transmission processing section 1402 and transmission
processing section 1405 carry out transmission processing on
transmission digital signal S72 of modulated signal A output from
data sequence generation section 1401 and transmission digital
signal S73 of modulated signal B output from data sequence
generation section 1401 respectively in accordance with
instructions from frame generation instruction section 401. Since
transmission processing section 1402 and transmission processing
section 1405 have the same internal configuration, only the
internal configuration of transmission processing section 1402 will
be explained.
[0143] S/P conversion section 1403 converts serial signal S74
output from modulation section 4031 to parallel signal S75 and
outputs converted parallel signal S75 to IDFT section 1404.
[0144] IDFT section 1404 performs an Inverse Discrete Fourier
Transform on parallel signal S75 output from S/P conversion section
1403 and thereby forms OFDM signal S76 and outputs formed OFDM
signal S76 to radio section 4033.
[0145] FIG. 18 is a block diagram showing the configuration of a
communication terminal apparatus according to Embodiment 3 of the
present invention. However, components of FIG. 18 common to FIG. 6
are assigned the same reference numerals as those in FIG. 6 and
detailed explanations thereof will be omitted.
[0146] Radio section 501 carries out predetermined radio processing
(down-conversion and A/D conversion or the like) on signal S90
received by antenna 252 and outputs signal S91 after the radio
processing to DFT section 1501 and reception field intensity
estimation section 1509.
[0147] DFT section 1501 performs a Discrete Fourier Transform on
signal S91 output from radio section 501 and outputs signal S92
after the conversion to first channel fluctuation estimation
section 1502, second channel fluctuation estimation section 1503
and demodulation section 1507.
[0148] Using radio wave propagation environment estimation symbols
of modulated signal A out of signal S92 output from DFT section
1501, first channel fluctuation estimation section 1502 estimates a
channel fluctuation of modulated signal A, that is, estimates a
channel condition. The channel fluctuation information of estimated
modulated signal A is output from first channel fluctuation
estimation section 1502 to demodulation section 1507 as channel
fluctuation estimation signal S93. Using radio wave propagation
environment estimation symbols of modulated signal B out of signal
S92 output from DFT section 1501, second channel fluctuation
estimation section 1503 estimates a channel fluctuation of
modulated signal B (channel condition) The estimated channel
fluctuation information of modulated signal B is output from second
channel fluctuation estimation section 1503 to demodulation section
1507 as channel fluctuation estimation signal S94. Channel
fluctuation signals S93 and S94 output from first channel
fluctuation estimation section 1502 and second channel fluctuation
estimation section 1503 include channel fluctuation information on
carriers 1 to 4.
[0149] Signal S95 received by antenna 253 is subjected to
processing similar to the above described processing by radio
section 506, DFT section 1504, first channel fluctuation estimation
section 1505 and second channel fluctuation estimation section
1506, and therefore detailed explanations thereof will be
omitted.
[0150] Demodulation section 1507 demodulates signals S92 and S97
output from DFT section 1501 and DFT section 1504 using channel
fluctuation information S93, S94, S98, S99 output from first
channel fluctuation estimation sections 1502 and 1505 and second
channel fluctuation estimation sections 1503 and 1506. At this
time, demodulation section 1507 acquires a transmission method (X
or Y) of the signal, modulation scheme and error correcting scheme
from transmission method report symbols of signals S92 and S97
output from DFT section 1501 and DFT section 1504, demodulates data
symbols in accordance with the acquired contents and obtains
received digital signal S100 of modulated signal A and received
digital signal S101 of modulated signal B. Demodulation is
performed based on relation equations of Equation (1) and Equation
(2). The demodulated signal is output from demodulation section
1507 as received digital signals S100 and S101 and output to
reception quality estimation section 1508 as well.
[0151] Reception quality estimation section 1508 calculates a bit
error rate, packet loss rate, frame error rate or the like based on
signals S100 and S101 output from demodulation section 1507 and
estimates reception quality according to them. The estimation
result is output from reception quality estimation section 1508 to
transmission method determining section 1510 and modulation scheme
determining section 1511 as reception quality estimation signal
S102
[0152] Reception field intensity estimation section 1509 estimates
reception field intensity based on signals S91 and S96 output from
radio section 501 and radio section 506 and outputs the estimation
result to transmission method determining section 1510 and
modulation scheme determining section 1511 as reception field
intensity estimation signal S103.
[0153] Transmission method determining section 1510 determines
transmission method X or transmission method Y to be requested from
the base station apparatus based on reception quality estimation
signal S102 output from reception quality estimation section 1508
and reception field intensity estimation signal S103 output from
reception field intensity estimation section 1509 at a
predetermined timing which will be described later and outputs the
transmission method as transmission method request information. For
example, transmission method determining section 1510 determines
transmission method X when the reception field intensity is
secured, yet the reception quality cannot be secured, while
determines transmission method Y when the reception quality for the
reception field intensity can be secured sufficiently.
[0154] Modulation scheme determining section 1511 determines a
modulation scheme to be requested from the base station apparatus
at a predetermined timing which will be described later based on
reception quality estimation signal S102 output from reception
quality estimation section 1508 and reception field intensity
estimation signal S103 output from reception field intensity
estimation section 1509. The determined scheme is output from the
communication terminal apparatus as modulation scheme request
information. The modulation scheme request information and
transmission method request information are transmitted to the base
station apparatus.
[0155] Next, the operations of the base station apparatus and
communication terminal apparatus having the above described
configurations will be explained. FIG. 19 illustrates a sequence
diagram of a communication procedure of a base station apparatus
and communication terminal apparatus according to Embodiment 3 of
the present invention. In this figure, in ST1601, the communication
terminal apparatus requests the base station apparatus to start a
communication and the base station apparatus receives this
request.
[0156] In ST1602, the base station apparatus receives the
communication start request sent in ST1601 and transmits radio wave
propagation environment estimation symbols and data symbols to the
communication terminal apparatus using transmission method X and
under a modulation scheme of BPSK. This makes it possible to
improve reception quality of data symbols immediately after a
communication is started and realize high demodulation accuracy at
the communication terminal apparatus.
[0157] Following ST1603 to ST1609 correspond to ST603 to ST609 in
FIG. 8, and therefore detailed explanations thereof will be
omitted.
[0158] FIG. 20 illustrates a transmission method and modulation
scheme applied by the base station apparatus changing with
time-shift in such a series of communication procedures. Here,
suppose three modulation schemes QPSK, 16 QAM, 64 QAM are used. In
this figure, a communication between the base station apparatus and
communication terminal apparatus starts at time t0 and transmission
method X and BPSK are forcibly used from time t1 to t3. At time t2,
the communication terminal apparatus requests to change the
transmission method and modulation scheme, and at time t3, only the
modulation scheme is changed from BPSK to 16 QAM and transmission
method X and 16 QAM are used from time t3 to t5. Furthermore, at
time t4, the communication terminal apparatus requests to change
only the modulation scheme, and at time t5, only the modulation
scheme is changed again from 16 QAM to 64 QAM. From time t5 to t6,
transmission method X and 64 QAM are used and at time t7, the
communication ends.
[0159] Furthermore, when the base station apparatus and
communication terminal apparatus start a communication at time t8,
transmission method X and BPSK are forcibly used from time t9 to
t11. At time t10, the communication terminal apparatus requests to
change the transmission method and modulation scheme, and at time
t11, the transmission method is changed from X to Y and the
modulation scheme is changed from BPSK to 16 QAM and transmission
method Y and 16 QAM are used from time t11 to t13. Furthermore, at
time t12, the communication terminal apparatus requests to change
only the modulation scheme, and at time t13, only the modulation
scheme is changed again from 16 QAM to QPSK. From time t13 to t14,
transmission method Y and QPSK are used and at time t15, the
communication ends.
[0160] In this way, using forcibly transmission method X and BPSK
obtaining high error resistance and high reception quality at the
start of a communication the base station apparatus is capable of
simplifying the communication procedure from the beginning of
communication to data transmission, and the communication terminal
apparatus is capable of reliably demodulating data immediately
after the communication start.
[0161] Thus, according to this embodiment, the base station
apparatus and communication terminal apparatus are provided with a
plurality of antennas respectively, forcibly applies at the start
of a communication any one of the transmission methods and
modulation schemes having strong error resistance out of a first
transmission method transmitting a first modulated signal and
second modulated signal including the same data from a plurality of
antennas and a second transmission method transmitting a third
modulated signal and a fourth modulated signal including different
data from a plurality of antennas. And therefore, it is possible to
simplify the communication procedure from the start of the
communication to data transmission, and the communication terminal
apparatus is capable of reliably demodulating the data immediately
after the communication start. Furthermore, it is also possible to
improve the data transmission rate and transmission quality under
an OFDM scheme.
[0162] This embodiment has explained the case where the
transmission method and modulation scheme are fixed at the start of
a communication, but it is also possible to fix only the
transmission method and make the modulation scheme selectable.
[0163] Furthermore, this embodiment selects the transmission method
and modulation scheme based on reception quality such as a bit
error rate, packet loss rate and frame error rate, but it is also
possible to select the transmission method and modulation scheme
based on eigenvalues of the channel matrix explained in Embodiment
1.
Embodiment 4
[0164] Embodiment 3 has explained the case where the transmission
method is changed only once during a communication without
selecting the transmission method and modulation scheme at the
start of a communication, but Embodiment 4 of the present invention
will explain a case where a transmission method is changed at
predetermined time intervals during a communication.
[0165] Since the configurations of the base station apparatus and
communication terminal apparatus are the same as those in
Embodiment 3, FIG. 17 and FIG. 18 will be used and detailed
explanations thereof will be omitted.
[0166] FIG. 21 is a sequence diagram of a communication procedure
of a base station apparatus and communication terminal apparatus
according to Embodiment 4 of the present invention. Note that only
ST1906 and ST1907 in this figure are different from ST1606 and
ST1607 in FIG. 19, and the rest of the procedure is the same as
that in FIG. 19. Therefore, only ST1906 and ST1907 will be
explained.
[0167] In ST1906, after a predetermined time passes from the start
of a communication, the communication terminal apparatus determines
a transmission method and modulation scheme applied by the base
station apparatus and requests the determined contents from the
base station apparatus. The base station apparatus receives this
request.
[0168] In ST1907, the base station apparatus determines the
transmission method and modulation scheme based on the request
transmitted from the communication terminal apparatus and reports
the determined transmission method and modulation scheme to the
communication terminal apparatus using transmission method report
symbols.
[0169] FIG. 22 illustrates the transmission method and modulation
scheme applied by the base station apparatus changing with
time-shift in such a series of communication procedures. Here,
three modulation schemes QPSK, 16 QAM, 64 QAM are supposed to be
used. In this figure, at time t0, a communication between the base
station apparatus and communication terminal apparatus starts and
from time t1 to t3, transmission method X and BPSK are forcibly
used. At time t2, the communication terminal apparatus requests to
change the transmission method from X to Y and to change the
modulation scheme from BPSK to 16 QAM, and from time t3 to t5,
transmission method Y and 16 QAM are used. Furthermore, at time t4,
the communication terminal apparatus requests to change only the
modulation scheme from 16 QAM to 64 QAM and from time t5 to t6,
transmission method Y and 64 QAM are used.
[0170] At time t6, the communication terminal apparatus requests to
change the transmission method and modulation scheme, requesting to
change the transmission method from Y to X, while to maintain the
modulation scheme of 64 QAM.
[0171] At time t7, the transmission method is changed during a
communication and from time t7 to t9, transmission method X and 64
QAM are used.
[0172] At time t8, the communication terminal apparatus requests to
change only the modulation scheme from 64 QAM to 16 QAM, and from
time t9 to t11, transmission method X and 16 QAM are used.
Furthermore, at time t10, the communication terminal apparatus
request to change only the modulation scheme from 16 QAM to QPSK
again, and from time t11 to t12, transmission method X and QPSK are
used and at time t13, and then the communication ends.
[0173] Thus, by changing the transmission method during a
communication at predetermined time intervals, it is possible to
respond to a change of the propagation path model. Note that the
predetermined time intervals should be such intervals that the
transmission method is not changed unnecessarily.
[0174] In this way, according to this embodiment, when a
communication takes a long time, the propagation model may change.
And by changing the transmission method during the communication,
it is possible to improve both reception quality and the increase
of transmission rate even when the propagation model changes during
the communication.
[0175] Embodiment 3 and Embodiment 4 explains an OFDM scheme and
the present invention is not limited to this and it is possible to
add a spreading section and implement the present invention
likewise under an OFDM scheme using a spread spectrum scheme. The
present invention can also be implemented under multicarrier
schemes other than the OFDM scheme.
Embodiment 5
[0176] Embodiments 1 to 4 have explained the case where a scheme
using space-time block codes or space-time trellis codes is used as
transmission method X and a scheme for simultaneously transmitting
a plurality of different data as shown in Equation (2) is used as
transmission method Y. Embodiment 5 of the present invention will
explain a transmission method capable of obtaining a diversity gain
such as Cyclic Delay Diversity (CDD) as transmission method X which
is different from space-time block codes and space-time trellis
codes.
[0177] Hereinafter, CDD will be explained using FIG. 23. FIG. 23
illustrates a frame configuration when CDD is carried out using 12
symbols. In this figure, transmission signal A and transmission
signal B are frames transmitted from different antennas, for
example, transmission signal A is transmitted from antenna 202
shown in FIG. 4 and transmission signal B is transmitted from
antenna 203 shown in FIG. 4.
[0178] Transmission signal A is made up of symbols Sy1, Sy2, . . .
, Sy11, Sy12 in that order used for CDD and the respective symbols
are transmitted at times i+1, i+2, i+11, i+12.
[0179] Transmission signal B is obtained by making a cyclic shift
of 6 symbols from a symbol sequence of transmission signal A and
made up of Sy7, Sy8, . . . , Sy5, Sy6 in that order and the
respective symbols are transmitted at times i+1, i+2, . . . , i+11,
i+12.
[0180] Adopting such a frame configuration allows an equalizer of
the reception apparatus to acquire a diversity gain and thereby
improve data reception quality. Therefore, though CDD has a lower
transmission rate than that of transmission method Y, but have
better reception quality.
[0181] Therefore, Embodiments 1 to 4 can also be implemented using
CDD as the transmission method similar to space-time block codes or
space-time trellis codes.
Embodiment 6
[0182] Embodiment 5 has explained the scheme using CDD which is
different from space-time block codes and space-time trellis codes
as transmission method X. Embodiment 6 of the present invention
will further explain a case where a communication mode called an
"eigenmode" in an MIMO (Multiple-Input Multiple-Output) system as
transmission method X.
[0183] When channel state information which is a propagation
channel estimation result between both stations is already known
not only to the reception station but also to the transmission
station, the MIMO system can realize a communication method whereby
the transmission station transmits a signal vectorized using a
transmission channel signature vector to the reception station from
a transmission array antenna and the reception station detects and
demodulates the transmission signal using a reception channel
signature vector associated with the transmission channel signature
vector from the received signal of the reception array antenna.
[0184] In this MIMO system, an eigenmode using singular vectors or
eigen vectors of a channel matrix is available as a communication
mode that multiplexes and transmits signals configuring a plurality
of channels in a communication space (described, for example, in a
document "Eigen Beam Space Division Multiplexing (E-SDM) Scheme in
MIMO Channel" Institute of Electronics, Information and
Communication Engineers, TECHNICAL REPORT OF IEICE RCS2002-53, May
2002).
[0185] This eigenmode is a method of using these singular vectors
and eigen vectors as channel signature vectors. Here, the channel
matrix is a matrix whose elements consist of complex channel
coefficients which are a combination of some or all of antenna
elements of a transmission array antenna and antenna elements of a
reception array antenna.
[0186] FIG. 24 illustrates the configuration of a channel
multiplexing communication system using a beam space mode
represented by an eigenmode in an MIMO system. First, base station
apparatus 2300 will be explained. Multiplexed frame generation
section 2301 generates a plurality of transmission frames for
mapping a transmission data sequence input to multiplexing channels
and outputs the plurality of transmission frames generated to
vector multiplexing section 2303.
[0187] Transmission channel analysis section 2302 calculates a
plurality of transmission channel signature vectors to constitute
multiplexing channels based on channel state information between
base station apparatus 2300 and communication terminal apparatus
2310. Transmission channel analysis section 2302 outputs the
calculated transmission channel signature vectors to vector
multiplexing section 2303.
[0188] Vector multiplexing section 2303 multiplies the respective
transmission frames output from multiplexed frame generation
section 2301 by different channel signature vectors output from
transmission channel analysis section 2302 and combines the
transmission frames. Vector multiplexing section 2303 transmits the
combined signal to communication terminal apparatus 2310 through
transmission array antenna 2304.
[0189] Next, communication terminal apparatus 2310 will be
explained. Reception channel analysis section 2311 calculates a
plurality of reception channel signature vectors to separate the
multiplexed transmission signal based on channel state information
between base station apparatus 2300 and communication terminal
apparatus 2310. Reception channel analysis section 2311 outputs the
calculated plurality of reception channel signature vectors to
multiplexed signal separation section 2313.
[0190] Multiplexed signal separation section 2313 generates a
plurality of reception frames by multiplying a signal (received
signal) received through reception array antenna 2312 by the
respective channel signature vectors output from reception channel
analysis section 2311. Multiplexed signal separation section 2313
outputs a plurality of generated reception frames to multiframe
combination section 2314.
[0191] Multiframe combination section 2314 combines signals mapped
to the multiplexing channels and obtains a received data
sequence.
[0192] Here, assuming that base station apparatus 2300 has a
function of transmitting data by switching transmission method X
and transmission method Y, the configuration of the transmission
apparatus provided for base station apparatus 2300 is shown in FIG.
25. However, components of FIG. 25 common to and FIG. 5 are
assigned the same reference numerals and detailed explanations
thereof will be omitted.
[0193] In FIG. 25, when transmission method request information
indicates transmission method X, that is, an eigenmode, signal
processing section 2401 applies the above described signal
processing using channel state information from the other
communication party (communication terminal apparatus 2310). On the
other hand, when the transmission method request information
indicates transmission method Y, that is, the transmission method
shown in Equation (2), signal processing section 2401 does not
apply any signal processing and outputs signal S5 as signal S110
and outputs signal S9 to as signal S111.
[0194] Thus, using an eigenmode enables the reception apparatus to
obtain good reception quality in a reception environment in which
direct waves are dominant. Therefore, it is also possible to
implement Embodiments 1 to 4 by using an eigenmode as a
transmission method similar to space-time block codes and
space-time trellis codes.
Embodiment 7
[0195] Embodiment 7 of the present invention will explain a method
of switching between the transmission method using an eigenmode
explained in Embodiment 6 and the transmission method shown in
Equation (2).
[0196] Examples of generally known communication modes include a
point-to-multi point type communication mode shown in FIG. 26A, a
point-to-point type communication mode shown in FIG. 26B and a
point-to-point type communication mode shown in FIG. 26C.
[0197] FIG. 26A shows that a base station is communicating with a
plurality of communication terminals simultaneously and FIG. 26B
shows that two communication terminals are communicating with each
other. Likewise, FIG. 26C shows that a base station is
communicating with one communication terminal.
[0198] However, the eigenmode has the following points that should
be improved. First, since the eigenmode needs to acquire channel
state information from the other communication party, when the base
station is communicating with a plurality of other communication
parties, it is necessary to acquire channel state information from
the plurality of the other communication parties respectively,
which deteriorates the data transmission efficiency. Second, when
eigen beams are formed for a plurality of other communication
parties, it is necessary to perform complicated signal
processing.
[0199] For these reasons, in a point-to-multi point type
communication mode in which there are a plurality of other
communication parties, it is not desirable to use eigenmode..
Therefore, the eigenmode is preferably used in a point-to-point
type communication mode.
[0200] That is, it is not necessary to consider the points to be
improved in above-mentioned eigenmode by using the eigenmode in the
point-to-point type communication mode, and it is possible to
increase the transmission rate and improve reception quality
compared to the use of the transmission method (transmission method
Y) shown in Equation (2). However, when the transmission method is
changed according to the number of other communication parties, it
is necessary to transmit the number of other communication parties
with which the subject station is communicating to the other
communication parties, and therefore it is necessary to insert
symbol of "information on the number of other communication
parties" in the transmission frame.
[0201] After the transmission method is set, as explained in
Embodiments 1 to 4, it is possible to make compatible the data
transmission rate with the transmission quality by changing the
modulation scheme. For the setting of the transmission method, the
methods explained in Embodiments 1 to 4 will be used.
[0202] Here, a further effect when the transmission method is
changed according to the number of other communication parties as
described above will be explained using FIG. 27. As shown in FIG.
27, in a cell of a base station which is communicating with two
communication terminals A and B, two other communication terminals
C and D can communicate in an eigenmode. This is because, according
to the transmission method using the eigenmode, an eigen beam is
formed directed to the other communication party, and therefore
interference with the base station and other communication
terminals A and B can be avoided. However, as shown in FIG. 28,
when communication terminals C and D carrying out a communication
using the eigenmode interfere with communication stations (base
station, communication terminals A and B in FIG. 28) carrying out
transmission method Y, an interrupt mode that forcibly terminates a
communication using the eigenmode (eigen beam communication) can be
set in a transmission signal of the base station.
[0203] Next, a communication procedure between the base station
apparatus and the communication terminal apparatus will be
explained. FIG. 29 illustrates a sequence diagram showing a
communication procedure of the base station apparatus and
communication terminal apparatus. In this figure, in ST2801, the
communication terminal apparatus requests the base station
apparatus to start communication and requests a transmission method
(transmission method using an eigenmode or transmission method
shown in Equation (2)) from the base station apparatus, and the
base station apparatus receives this request. Transmission method
requested by the communication terminal apparatus is particularly a
transmission method using an eigenmode when the communication
terminal apparatus desires a one-to-one (point-to-point,
peer-to-peer) communication with the other communication party.
[0204] The base station apparatus then changes the transmission
method in accordance with the current communication mode. That is,
the base station apparatus changes the transmission method
depending on whether or not a one-to-multi point communication is
being carried out. More specifically, the base station apparatus
determines the transmission method shown in Equation (2) when a
one-to-multi point communication is being carried out and
determines a transmission method using an eigenmode in the case of
a communication with only the communication terminal apparatus
which has received the request (point-to-point type) and in ST2802,
the base station apparatus reports the communication terminal
apparatus of the determined transmission method.
[0205] In ST2803, the communication terminal apparatus requests a
modulation scheme suitable for the determined transmission method
and the base station apparatus receives this request.
[0206] In ST2804, the base station apparatus determines the
modulation scheme based on the transmitted modulation scheme
request information and notifies the communication terminal
apparatus of the determined modulation scheme.
[0207] In ST2805, the base station apparatus transmits data to the
communication terminal apparatus using the transmission method
notified in ST2802 and the modulation scheme notified in
ST2804.
[0208] In ST2806, the communication terminal apparatus transmits
data to the base station apparatus using the communication scheme
and modulation scheme used for data communication in ST2805.
[0209] In ST2807, the base station apparatus sends a report to end
a communication to the communication terminal apparatus, and the
communication terminal apparatus receives this report, and the
communication ends.
[0210] Thus, according to this embodiment, a transmission method
using an eigenmode, which is transmission method X, is adopted in a
one-to-one communication, and transmission method Y, a transmission
method shown in Equation (2) is adopted in a one-to-multi point
communication. Therefore, it is possible to improve both the data
transmission rate and transmission quality as the system.
[0211] The above described embodiments explains the communication
terminal apparatus as an example of the reception apparatus and the
base station apparatus as an example of the transmission apparatus,
but the present invention is not limited to this and the
communication terminal apparatus may function as the transmission
apparatus and the base station apparatus may function as the
reception apparatus. Furthermore, in the above described
embodiments, the reception apparatus determines the transmission
method and modulation scheme, but the present invention is not
limited to this and the transmission apparatus may determine the
transmission method and modulation scheme by receiving reports of
eigenvalues and reception field intensity from the reception
apparatus.
[0212] Furthermore, in the above described embodiments, SyA and
SyA* which is a complex conjugate of SyA are transmitted as the
data symbols to be transmitted using transmission method X, but the
present invention is not limited to this and SyA may be repeated
and transmitted instead.
[0213] Furthermore, the above described embodiments explain
assuming that the number of transmission antennas and the number of
reception antennas are 2 respectively, but the present invention is
not limited to this and three or more transmission antennas and
reception antennas may be used. At this time, it goes without
saying that the number of transmission processing sections ahead of
the antenna of the transmission apparatus (e.g., modulation
section, spreading section, radio section and amplifier or the
like) at the base station apparatus matches the number of
transmission antennas. The same applies to the reception apparatus
at the communication terminal apparatus. It is also possible to
select any number of antennas from at least three antennas.
[0214] For example, the number of transmission antennas may be 4
and 4 lines of modulated signal may be transmitted from the 4
antennas. At this time, assuming that a method using space-time
coding is transmission method A and a method not using space-time
coding is transmission method B, it is possible to arbitrary select
any one of transmission method X and transmission method Y when two
transmission antennas are use, and any one of, transmission method
A and transmission method B. Note that even when the maximum value
of the number of modulated M-ary index of transmission method X and
transmission method Y is greater than the maximum value of the
number of modulated M-ary index of transmission method A and
transmission method B, there is no influence on the complexity of
the circuit configuration of the communication terminal
apparatus.
[0215] Furthermore, a plurality of antennas may be treated as one
set of antennas.
[0216] That is to say, there may be a plurality of antennas 202 and
antennas 203.
[0217] The transmission method of the present invention comprises a
transmission method determining step of determining anyone of a
first transmission method whereby a transmission apparatus provided
with a plurality of antennas transmits a plurality of signals
including the same data from a plurality of antennas and a second
transmission method whereby the transmission apparatus transmits a
plurality of signals including different data from the plurality of
antennas, a modulation scheme determining step of determining any
one of the plurality of modulation schemes and a control step of
controlling whether determining processing should be performed or
not in the transmission method determining step and the modulation
scheme determining step in accordance with a communication
procedure with the other communication party.
[0218] According to this method, it is possible to improve data
transmission efficiency by switching between the first transmission
method having strong error resistance and the second transmission
method having a high data transmission rate and switching the
modulation scheme in accordance with the communication procedure
with the other communication party.
[0219] In the above described transmission method of the present
invention, control is performed in the control step so that
determining processing is not carried out in the transmission
method determining step during data transmission and determining
processing is carried out only in the modulation scheme determining
step.
[0220] According to this method, both the transmission method and
modulation scheme are not determined, or changed during data
transmission, which requires less processing compared to the case
where both the transmission method and modulation scheme are
changed, and therefore it is possible to prevent a processing
burden of the system increasing.
[0221] In the above described transmission method of the present
invention, the modulation scheme used for the first transmission
method and the modulation scheme used for the second transmission
method have the same maximum value of the number of modulated M-ary
index.
[0222] According to this method, the amplitude variation range of
the modulated signal becomes larger as the number of modulated
M-ary index increases, and the power consumption of the
corresponding amplifier becomes greater as the amplitude variation
range of the modulated signal becomes larger. Therefore, by
equalizing the maximum value of the number of modulated M-ary index
applied to both of the first transmission method and the second
transmission method, it is possible to prevent power consumption of
the amplifier from increasing.
[0223] In the above described transmission method of the present
invention, the first transmission method or the second transmission
method are determined based on the channel fluctuation.
[0224] According to this method, since the second transmission
method is likely to deteriorate reception quality by receiving a
direct wave, it is possible to determine the first or second
transmission method based on the channel fluctuation, thereby avoid
deterioration of reception quality using the first transmission
method when a direct wave is received and improve the data
transmission efficiency using the second transmission method when a
direct wave is not received.
[0225] In the above described transmission method of the present
invention is designed to predetermine a transmission method to be
used at the start of a communication in the transmission method
determining step and a modulation scheme to be used at the start of
a communication in the modulation scheme determining step.
[0226] According to this method, by forcibly applying the
transmission method and modulation scheme with strong error
resistance at the start of a communication, it is possible to
simplify the communication procedure from the start of a
communication to data transmission and reliably demodulate the data
immediately after the communication start on the receiving
side.
[0227] In the above described transmission method of the present
invention, control in the control step is performed in such a way
that determining processing in the transmission method determining
step is carried out at longer time intervals than determining
processing carried out in the modulation scheme determining
step.
[0228] According to this method, the propagation model may change
when the communication time extends, and therefore by changing the
transmission method at longer time intervals than changing the
modulation scheme, it is possible to improve both reception quality
and the increase of the transmission rate even when the propagation
model changes during the communication.
[0229] In the above described transmission method of the present
invention is designed to use cyclic delay diversity as the first
transmission method in the transmission method determining
step.
[0230] In the above described transmission method of the present
invention is designed to use an eigenmode in which singular vectors
or eigen vectors of a channel matrix in an MIMO system are used as
channel signature vectors as the first transmission method in the
transmission method determining step.
[0231] According to these methods make it possible to improve data
transmission efficiency by adopting a transmission method using
cyclic delay diversity or eigenmode as the first transmission
method.
[0232] In the above described transmission method of the present
invention is designed to switch between the first transmission
method and the second transmission method in accordance with the
number of other communication parties in the transmission method
determining step.
[0233] According to this method, when the number of other
communication parties is, for example, 1, adopting the transmission
method using an eigenmode can reduce interference with other
communication stations, and when the number of other communication
parties is more than 1, adopting the second transmission method can
prevent the data transmission efficiency decreasing.
[0234] The communication system according to the present invention
is a radio communication system comprising a transmission apparatus
provided with a plurality of antennas and a reception apparatus
that receives signals transmitted from the plurality of antennas of
the transmission apparatus, wherein the reception apparatus
comprises a channel fluctuation estimation section that estimates a
channel fluctuation about signals transmitted from the plurality of
antennas of the transmission apparatus, a transmission method
requesting section that determines any one of a first transmission
method of transmitting a plurality of signals including the same
data from the plurality of antennas and a second transmission
method of transmitting a plurality of signals including different
data from the plurality of antennas based on the estimated channel
fluctuation and requests the determined transmission method from
the transmission apparatus, a modulation scheme requesting section
that determines any one of a plurality of modulation schemes based
on the estimated channel fluctuation and requests the determined
modulation scheme from the transmission apparatus and a control
section that controls whether or not the processing requested by
the transmission method requesting section and modulation scheme
requesting section should be performed in accordance with the
procedure for a communication with the transmission apparatus, and
the transmission apparatus comprises a generation section that
generates a signal corresponding to the transmission method
requested from the reception apparatus and a transmission
processing section that modulates a signal generated by the
generation section according to the modulation scheme requested
from the reception apparatus and transmits the modulated signal
from the respective antennas.
[0235] According to this configuration, switching between the first
transmission method having strong error resistance and the second
transmission method having a high data transmission rate and
switching between modulation schemes are performed based on the
estimation result of the channel fluctuation estimation section,
and therefore it is possible to improve the data transmission
efficiency and reception quality.
[0236] The transmission apparatus of the present invention
comprises a plurality of transmission antennas, a transmission
method determining section that determines any one of a first
transmission method of transmitting a plurality of signals
including the same data from the plurality of antennas and a second
transmission method of transmitting a plurality of signals
including different data from the plurality of antennas, a
modulation scheme determining section that determines any one of a
plurality of modulation schemes, a control section that controls
whether determining processing by the transmission method
determining section and modulation scheme determining section
should be performed or not in accordance with the procedure for a
communication with the other communication party and a transmission
processing section that transmits the signals to which the
determined transmission method and modulation scheme are applied
from the plurality of antennas.
[0237] According to this configuration, switching between the first
transmission method with strong error resistance and the second
transmission method with a high data transmission rate and
switching between the modulation schemes are performed in
accordance with the procedure for a communication with the other
communication party, and therefore it is possible to improve data
transmission efficiency.
[0238] In the transmission apparatus of the present invention in
the above described configuration, the control section controls in
such a way that the transmission method determining section does
not perform determining processing during data transmission and
only the modulation scheme determining section performs determining
processing.
[0239] According to this configuration, both the transmission
method and modulation scheme are not determined or changed during
data transmission, which requires less processing compared to the
case where both the transmission method and modulation scheme are
changed, and can thereby prevent a processing burden of the system
from increasing.
[0240] In the transmission apparatus of the present invention in
the above described configuration, the transmission processing
section adopts a modulation scheme having the same maximum value of
the number of modulated M-ary index for the modulation scheme used
for the first transmission method and the modulation scheme used
for the second transmission method.
[0241] According to this method, the amplitude variation range of
the modulated signal becomes larger as the number of modulated
M-ary index increases, and the power consumption of the
corresponding amplifier becomes greater as the amplitude variation
range of the modulated signal becomes larger. Therefore, by
equalizing the maximum value of the number of modulated M-ary index
applied to both of the first transmission method and the second
transmission method, it is possible to prevent power consumption of
the amplifier from increasing.
[0242] In the transmission apparatus of the present invention in
the above described configuration, the transmission method
determining section is configured predetermines the transmission
method to be used at the start of a communication and the
modulation scheme determining section predetermines the modulation
scheme to be used at the start of a communication.
[0243] According to this configuration, by forcibly applying the
transmission method and modulation scheme with strong error
resistance at the start of a communication, it is possible to
simplify the communication procedure from the start of a
communication to data transmission and reliably demodulate the data
immediately after the communication start on the receiving
side.
[0244] In the transmission apparatus of the present invention in
the above described configuration, the control section is
configured to control in such a way that the transmission method
determining section performs determining processing at longer time
intervals than the modulation scheme determining section performs
determining processing.
[0245] According to this configuration, the propagation model may
change when the communication time extends, and therefore by
changing the transmission method at longer time intervals than
changing the modulation scheme, it is possible to improve both
reception quality and the increase of the transmission rate even
when the propagation model changes during a communication.
[0246] In the transmission apparatus of the present invention in
the above described configuration, the transmission method
determining section is configured to use cyclic delay diversity as
the first transmission method.
[0247] In the transmission apparatus of the present invention in
the above described configuration, the transmission method
determining section is configured to use an eigenmode in which
singular vectors or eigen vectors of a channel matrix in an MIMO
system are used as channel signature vectors as the first
transmission method.
[0248] According to these configurations, it is possible to improve
data transmission efficiency by adopting a transmission method
using cyclic delay diversity or eigenmode as the first transmission
method.
[0249] In the transmission apparatus of the present invention in
the above described configuration, the transmission method
determining section is configured to switch between the first
transmission method and the second transmission method in
accordance with the number of other communication parties.
[0250] According to this configuration, when the number of other
communication parties is 1, adopting the transmission method using
an eigenmode makes it possible to reduce interference with other
communication stations, and when the number of other communication
parties is more than 1, adopting the second transmission method
makes it possible to prevent the data transmission efficiency from
decreasing.
[0251] The reception apparatus according to the present invention
comprises a transmission method determining section that determines
any one of a first transmission method of transmitting a plurality
of signals including the same data from a plurality of antennas and
a second transmission method of transmitting a plurality of signals
including different data from the plurality of antennas, a
modulation scheme determining section that determines any one of a
plurality of modulation schemes, a control section that controls
whether or not the determining processing by the transmission
method determining section and modulation scheme determining
section should be performed in accordance with the procedure for a
communication with the other communication party and a requesting
section that requests the determined transmission method and
modulation scheme from the other communication party.
[0252] According to this configuration, switching between the first
transmission method having strong error resistance and the second
transmission method having a high data transmission rate and
switching between the modulation schemes in accordance with the
procedure for a communication with the other communication party,
and therefore it is possible to improve the data transmission
efficiency.
[0253] In the reception apparatus of the present invention in the
above described configuration, the control section performs control
in such a way that the transmission method determining section does
not perform determining processing during data reception and only
the modulation scheme determining section performs determining
processing.
[0254] According to this configuration, both the transmission
method and modulation scheme are not determined or changed during
data reception, which requires less processing compared to the case
where both the transmission method and modulation scheme are
changed, and therefore, it is possible to prevent a processing
burden of the system from increasing.
[0255] The reception apparatus of the present invention in the
above described configuration comprises a channel fluctuation
estimation section that estimates both or any one of a channel
fluctuation and reception field intensity of the received signal,
wherein the transmission method determining section determines the
transmission method based on the estimation result estimated by the
channel fluctuation estimation section.
[0256] According to this configuration, the requesting section
determines any one of the first transmission method having strong
error resistance and the second transmission method having a high
data transmission rate based on the channel fluctuation estimated
for the received signal or reception field intensity, and can
thereby improve data transmission efficiency and reception
quality.
[0257] In the reception apparatus of the present invention in the
above described configuration, the modulation scheme used for the
first transmission method and the modulation scheme used for the
second transmission method are configured to have the same maximum
value of the number of modulated M-ary index.
[0258] According to this method, the amplitude variation range of
the modulated signal becomes larger as the number of modulated
M-ary index increases, and the power consumption of the
corresponding amplifier becomes greater as the amplitude variation
range of the modulated signal becomes larger. Therefore, by
equalizing the maximum value of the number of modulated M-ary index
applied to both of the first transmission method and the second
transmission method, it is possible to prevent power consumption of
the amplifier from increasing. Furthermore, the reception apparatus
need not process signals having a large amplitude variation range,
and can thereby simplify the circuit configuration.
[0259] According to the present invention, the transmission
apparatus comprises a plurality of antennas, determines any one of
a first transmission method of transmitting a plurality of signals
including the same data from a plurality of antennas and a second
transmission method of transmitting a plurality of signals
including different data from the plurality of antennas based on a
channel fluctuation between the transmitting and receiving sides
and determines, when determining any one of a plurality of
modulation schemes, only a modulation scheme out of the
transmission method and modulation scheme from the start to end of
a communication, and therefore, it is possible to thereby improve
the data transmission rate and reception quality together.
[0260] This application is based on Japanese Patent Application No.
2003-188898 filed on Jun. 30, 2003 and Japanese Patent Application
No. 2004-190418 filed on Jun. 28, 2004, entire content of which is
expressly incorporated by reference herein.
INDUSTRIAL APPLICABILITY
[0261] The present invention is suitable for use in a base station
apparatus and communication terminal apparatus having a plurality
of antennas.
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